Recent developments in particular in the field of natural gas exploitation are aiming to compress natural gas below sea-level directly at the well-head. Theses developments are economically very interesting because offshore platforms involve extremely high costs for operating personal. Underwater compression of natural gas might in future make mend offshore platforms superfluous.
However, the new development goes along with enormous technical problems connected with difficult operating conditions and bad accessibility of the compression units. Major challenges are low temperatures near the freezing point, high pressure of the surrounding chemically aggressive seawater, non-purified and chemically aggressive fluid to compress, wherein the natural gas varies in the suction-pressure and carries next to foreign particles also non-gaseous fluids respectively liquids in significant amounts. Over the life-time of the well, the pressure of the natural gas to be exploited decreases significantly. According to environmental protection no media exchange between the compressor unit and the surrounding is admitted.
International patent application WO01/50024 A proposes to provide a detection device in the suction line of a compressor unit to detect for particles or amount of liquid by a density meter and to change operation of the compressor accordingly. However, this might not be sufficient since big amounts of water still can destroy the compressor when entering the impeller.